A Bubble Dynamics Based Approach to the Simulation of Cavitation in Lubricated Contacts

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Thomas Geike ◽  
Valentin L. Popov
Keyword(s):  
Numerical Simulations ◽  
Experimental Evidence ◽  
Reynolds Equation ◽  
Bubble Dynamics ◽  
Simulation Models ◽  
Compressible Fluids ◽  
Fluid Film ◽  
Tensile Stresses ◽  
Lubricated Contacts

The negative squeeze lubrication problem is investigated by means of numerical simulations that account for the dynamics of vaporization. The model is based on bubble dynamics, governed by the Rayleigh–Plesset equation, and the Reynolds equation for compressible fluids. Unlike most existing simulation models our model can predict tensile stresses in the fluid film prior to its rupture, which is in accordance with experimental evidence.

scholarly journals BUBBLE DYNAMICS-BASED MODELING OF THE CAVITATION DYNAMICS IN LUBRICATED CONTACTS

2021 ◽  
Vol 19 (1) ◽  
pp. 115
Author(s):  
Thomas Geike
Keyword(s):  
Reynolds Equation ◽  
Bubble Dynamics ◽  
Bubble Formation ◽  
Additional Term ◽  
Fluid Machinery ◽  
Short Term ◽  
Tensile Stresses ◽  
Lubricated Contacts ◽  
Viscosity Term ◽  
Material Wear

Cavitation is a common phenomenon in fluid machinery and lubricated contacts. In lubricated contacts, there is a presumption that the short-term tensile stresses at the onset of bubble formation have an influence on material wear. To investigate the duration and magnitude of tensile stresses in lubricating films using numerical simulation, a suitable simulation model must be developed. The chosen simulation approach with bubble dynamics is based on the coupling of the Reynolds equation and Rayleigh-Plesset equation (introduced about 20 years ago by Someya).Following the basic approach from the author’s earlier papers on the negative squeeze motion with bubble dynamics for the simulation of mixed lubrication of rough surfaces, the paper at hand shows modifications to the Rayleigh-Plesset equation that are required to get the time scale for the dynamic processes right. This additional term is called the dilatational viscosity term, and it significantly influences the behavior of the numerical model. 

A Hydrodynamic Theory of Radial-Face Mechanical Seals

1973 ◽  
Vol 15 (1) ◽  
pp. 17-24 ◽  
Author(s):  
B. Stanghan-Batch ◽  
E. H. Iny
Keyword(s):  
Experimental Evidence ◽  
Reynolds Equation ◽  
Hydrodynamic Lubrication ◽  
Fluid Pressure ◽  
Fluid Film ◽  
Hydrodynamic Theory ◽  
Mechanical Seal ◽  
Mechanical Seals ◽  
Substantial Agreement ◽  
Seal Design

The existence of a lubricating fluid film between the faces of a mechanical seal has been amply demonstrated, but the mechanisms of lubrication and sealing have yet to be convincingly established. Experimental evidence to show that mechanical seal faces are most probably lubricated by a hydrodynamic action induced by the waviness of one of the surfaces has recently been published by the authors. Following this work a modified form of the narrow bearing approximation to Reynolds' equation for hydrodynamic lubrication has been applied to an idealized wavy faced seal. The resulting theory of seal face lubrication has been extended to include radial flows in the fluid film and predicts a net inward flow of fluid which may be utilized to oppose the flow due to the sealed fluid pressure. Predicted lubrication and sealing characteristics are in substantial agreement with measured values. It is suggested that the performance of mechanical seals can be improved by giving one face an appropriately wavy surface at the time of manufacture; a number of other observations on mechanical seal design are also made.

Theoretical Condition for the Cxy=Cyx Relation in Fluid Film Journal Bearings

1989 ◽  
Vol 111 (3) ◽  
pp. 426-429 ◽  
Author(s):  
T. Kato ◽  
Y. Hori
Keyword(s):  
Reynolds Equation ◽  
Journal Bearing ◽  
Journal Bearings ◽  
Fluid Film ◽  
Finite Width ◽  
Damping Coefficients ◽  
Dynamic Coefficients ◽  
Cross Terms ◽  
Linear Damping ◽  
Theoretical Condition

A computer program for calculating dynamic coefficients of journal bearings is necessary in designing fluid film journal bearings and an accuracy of the program is sometimes checked by the relation that the cross terms of linear damping coefficients of journal bearings are equal to each other, namely “Cxy = Cyx”. However, the condition for this relation has not been clear. This paper shows that the relation “Cxy = Cyx” holds in any type of finite width journal bearing when these are calculated under the following condition: (I) The governing Reynolds equation is linear in pressure or regarded as linear in numerical calculations; (II) Film thickness is given by h = c (1 + κcosθ); and (III) Boundary condition is homogeneous such as p=0 or dp/dn=0, where n denotes a normal to the boundary.

scholarly journals Tuning membrane content of sound absorbing cellular foams: Fabrication, experimental evidence and multiscale numerical simulations

2019 ◽  
Vol 162 ◽  
pp. 345-361 ◽  
Author(s):  
Van Hai Trinh ◽  
Vincent Langlois ◽  
Johann Guilleminot ◽  
Camille Perrot ◽  
Yacine Khidas ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Experimental Evidence ◽  
Cellular Foams

Two Dimensional Modified Reynolds Equation Including Pressure Dependent Viscosity Effect

2012 ◽  
Author(s):  
Jung Gu Lee ◽  
Alan Palazzolo
Keyword(s):  
Reynolds Equation ◽  
Elastohydrodynamic Lubrication ◽  
Fluid Film ◽  
Maximum Pressure ◽  
Elastic Solids ◽  
Pressure Distributions ◽  
Pressure Dependent Viscosity ◽  
Modified Reynolds Equation ◽  
Dependent Viscosity ◽  
Modified Equation

The Reynolds equation plays an important role for predicting pressure distributions for fluid film bearing analysis, One of the assumptions on the Reynolds equation is that the viscosity is independent of pressure. This assumption is still valid for most fluid film bearing applications, in which the maximum pressure is less than 1 GPa. However, in elastohydrodynamic lubrication (EHL) where the lubricant is subjected to extremely high pressure, this assumption should be reconsidered. The 2D modified Reynolds equation is derived in this study including pressure-dependent viscosity, The solutions of 2D modified Reynolds equation is compared with that of the classical Reynolds equation for the ball bearing case (elastic solids). The pressure distribution obtained from modified equation is slightly higher pressures than the classical Reynolds equations.

Numerical and Experimental Investigations on Preload Effects in Air Foil Journal Bearings

2017 ◽  
Author(s):  
Marcel Mahner ◽  
Pu Li ◽  
Andreas Lehn ◽  
Bernhard Schweizer
Keyword(s):  
Reynolds Equation ◽  
Journal Bearing ◽  
Journal Bearings ◽  
Compressible Fluids ◽  
Experimental Investigations ◽  
Hysteresis Curves ◽  
Numerical Predictions ◽  
Bearing Stiffness ◽  
Gasdynamic Model ◽  
Good Agreement

A detailed elasto-gasdynamic model of a preloaded three-pad air foil journal bearing is presented. Bump and top foil deflections are herein calculated with a nonlinear beamshell theory according to Reissner. The 2D pressure distribution in each bearing pad is described by the Reynolds equation for compressible fluids. With this model, the influence of the assembly preload on the static bearing hysteresis as well as on the aerodynamic bearing performance is investigated. For the purpose of model validation, the predicted hysteresis curves are compared with measured curves. The numerically predicted and the measured hysteresis curves show a good agreement. The numerical predictions exhibit that the assembly preload increases the bearing stiffness (in particular for moderate shaft displacements) and the bearing damping.

scholarly journals An Assessment of Quantitative Predictions of Deterministic Mixed Lubrication Solvers

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Yuechang Wang ◽  
Abdel Dorgham ◽  
Ying Liu ◽  
Chun Wang ◽  
Mark C. T. Wilson ◽  
...  
Keyword(s):  
Reynolds Equation ◽  
Thickness Distribution ◽  
Computation Time ◽  
Simulation Method ◽  
Coefficient Matrix ◽  
Mixed Lubrication ◽  
Contact Ratio ◽  
Lubricated Contacts ◽  
Discretization Schemes ◽  
Parametric Studies

Abstract The ability to simulate mixed lubrication problems has greatly improved, especially in concentrated lubricated contacts. A mixed lubrication simulation method was developed by utilizing the semi-system approach which has been proven to be highly useful for improving stability and robustness of mixed lubrication simulations. Then different variants of the model were developed by varying the discretization schemes used to treat the Couette flow terms in the Reynolds equation, varying the evaluation of density derivatives and varying the contribution of terms in the coefficient matrix. The resulting pressure distribution, film thickness distribution, lambda ratio, contact ratio, and the computation time were compared and found to be strongly influenced by the choice of solution scheme. This indicates that the output from mixed lubrication solvers can be readily used for qualitative and parametric studies, but care should be taken when making quantitative predictions.

scholarly journals Motion of a tightly fitting axisymmetric object through a lubricated elastic tube

2021 ◽  
Vol 926 ◽  
Author(s):  
Bhargav Rallabandi ◽  
Jens Eggers ◽  
Miguel Angel Herrada ◽  
Howard A. Stone
Keyword(s):  
Numerical Simulations ◽  
Numerical Solutions ◽  
Elastic Tube ◽  
Direct Numerical Simulations ◽  
Fluid Film ◽  
Square Root ◽  
Membrane Tension ◽  
Relative Speed ◽  
Thin Fluid ◽  
Thin Fluid Film

We consider the translation of a rigid, axisymmetric, tightly fitting object through a cylindrical elastic tube filled with viscous fluid, using a combination of theory and direct numerical simulations. The intruding object is assumed to be wider than the undeformed tube radius, forcing solid–solid contact in the absence of relative motion. The motion of the object establishes a thin fluid film that lubricates this contact. Our theory couples lubrication theory to a geometrically nonlinear membrane description of the tube's elasticity, and applies to a slender intruding object and a thin tube with negligible bending rigidity. We show using asymptotic and numerical solutions of the theory, that the thickness of the thin fluid film scales with the square root of the relative speed for small speeds, set by a balance of hoop stresses, membrane tension and fluid pressure. While membrane tension is relatively small at the entrance of the film, it dominates near the exit and produces undulations of the film thickness, even in the limit of vanishing speeds and slender objects. We find that the drag force on the intruding object depends on the slope of its surface at the entrance to the thin fluid film, and scales as the square root of the relative speed. The predictions of the lubricated membrane theory for the shape of the film and the force on the intruder are in quantitative agreement with three-dimensional direct numerical simulations of the coupled fluid–elastic problem.

LOW DIMENSIONAL NON-CRYSTALLOGRAPHIC METALLIC NANOSTRUCTURES: HRTEM SIMULATION, MODELS AND EXPERIMENTAL RESULTS

2006 ◽  
Vol 20 (13) ◽  
pp. 725-751 ◽  
Author(s):  
J. L. RODRÍGUEZ-LÓPEZ ◽  
J. M. MONTEJANO-CARRIZALES ◽  
M. JOSÉ-YACAMÁN
Keyword(s):  
Experimental Evidence ◽  
Bimetallic Nanoparticles ◽  
Size Range ◽  
Simulation Models ◽  
Platonic Solid ◽  
Gold Nanocrystals ◽  
Metallic Particles ◽  
Bimetallic Nanoparticle ◽  
Equilibrium Shapes ◽  
Low Dimensional

Modern nanoparticle research in the field of small metallic systems has confirmed that many nanoparticles take on some Platonic and Archimedean solids related shapes. A Platonic solid looks the same from any vertex, and intuitively they appear as good candidates for atomic equilibrium shapes. A very clear example is the icosahedral ( I h ) particle that only shows {111} faces that contribute to produce a more rounded structure. Indeed, many studies report the I h as the most stable particle at the size range r≤20 Å for noble gases and for some metals. In this review, we report on the structure and shape of mono- and bimetallic nanoparticles in the wide size range from 1–300 nm. First, we present AuPd nanoparticles in the 1–2 nm size range that show dodecahedral atomic growth packing, one of the Platonic solid shapes that have not been identified before in this small size range for metallic particles. Next, with particles in the size range of 2–5 nm, we present an energetic surface reconstruction phenomenon observed also on bimetallic nanoparticle systems of AuPd and AuCu , similar to a re-solidification effect observed during cooling process in lead clusters. These binary alloy nanoparticles show the fivefold edges truncated, resulting in {100} faces on decahedral structures, an effect largely envisioned and reported theoretically, with no experimental evidence in the literature before. Next nanostructure we review is a monometallic system in the size range of ≈5 nm that we termed the decmon. We present here some detailed geometrical analysis and experimental evidence that supports our models. Finally, in the size range of 100–300 nm, we present icosahedrally derived star gold nanocrystals which resembles the great stellated dodechaedron, which is a Kepler–Poisont solid. We conclude then that the shape or morphology of some mono- and bimetallic particles evolves with size following the sequence from atoms to the Platonic solids, and with a slightly greater particle's size, they tend to adopt Archimedean related shapes. If the particle's size is still greater, they tend to adopt shapes beyond the Archimedean (Kepler–Poisont) solids, reaching at the very end the bulk structure of solids. We demonstrate both experimentally and by means of computational simulations for each case that this structural atomic growth sequence is followed in such mono- and bimetallic nanoparticles.

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